Method  for preparing recycled low-nickel magnesium alloy using magnesium scraps

ABSTRACT

The present invention relates to a method for preparing a recycled low-nickel magnesium alloy using magnesium scraps. More particularly, the recycled magnesium alloy having a reduced nickel content can be prepared by adding Al and misch metal to molten magnesium scraps so as to form an Ni—Al-misch metal three-phase alloy or cluster thereof; and separating and removing the formed Ni—Al-misch metal three-phase alloy or the cluster thereof using gravity.

FIELD OF THE INVENTION

The present invention relates to a method for preparing a recycled low-nickel magnesium alloy using magnesium scraps. More particularly, it relates to a method for preparing a recycled magnesium alloy, which has a reduced nickel content, by adding Al and misch metal to molten magnesium scraps so as to form an Ni—Al-misch metal three-phase alloy or cluster thereof; and separating and removing the formed Ni—Al-misch metal three-phase alloy or the cluster thereof using gravity.

BACKGROUND OF THE INVENTION

In recent, demands of magnesium alloy, which is applied as vehicle and 3C parts, are largely increasing in concert with increased environment load and electric car development issues.

According to a growing trend in magnesium alloy use, potential of generation of scraps, which are recovered from discarded products whose life has expired, is increasing, and particularly, as magnesium products are mainly manufactured by gravity casting method or die casting method, many scarps are generated as a by-product due to the nature of the methods.

Techniques for recycling high grade scraps such as runner and overflow, which are generated in the process of manufacturing die casting parts, were already commercialized, but there is no technique for recycling scraps, which are recovered from cars and electronic parts whose life have expired, and therefore, development of related techniques is urgent.

When recycling low grade magnesium scraps such as car waste, there are advantages that raw material cost can be directly reduced because recycled ingot can be supplied at the price of 70˜80% of primary ingot, and also indirect cost by landfill can be reduced at the same time. Further, energy consumption and carbon dioxide generation in the process of producing the recycled ingot can be reduced as much as 30% or more, compared to the process of producing the primary ingot. Thus, it is expected to reduce environment load and energy.

In general, recycling process for obtaining magnesium metal from magnesium scraps contains the steps of: washing and crushing sorted scraps, or directly melting the classified scraps in a melting furnace, and then purifying impurities followed by casting to an ingot.

Magnesium (Mg) alloy for casting is dominated by AM (Mg—Al—Mn)- and AZ (Mg—Al—Zn)-based alloy, and in the magnesium alloy, aluminum (Al) has an effect of improving mechanical properties by refining cast structure of magnesium, zinc (Zn) has an effect of improving strength and castability, and manganese (Mn) has an effect of improving corrosion resistance. Accordingly, 6 to 10% of Al, 1 to 3% of Zn and about 0.3% of Mn are added to general magnesium alloy, sometimes small amount of zirconium (Zr) or rare-earth metal are added thereto, and small amount of iron (Fe), nickel (Ni), copper (Cu), silicon (Si) and the like are usually contained as impurities therein.

Accordingly, when manufacturing an ingot by remelting the recovered magnesium scraps, those elements are mixed and thereby largely deteriorating performance of recycled products. Thus it is necessary to develop essential techniques for controlling composition of those elements. Currently, techniques for recycling low grade magnesium scraps and techniques for controlling harmful elements are in the initial stage of technical development at home and abroad.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the above-described problems associated with prior art.

The present invention is objected to provide a novel method for preparing a recycled magnesium alloy, wherein the nickel content is reduced, using magnesium scraps.

In order to accomplish one object of the present invention, provided is a method for preparing a recycled low-nickel magnesium alloy using magnesium scraps, which comprises the steps of:

-   -   (a) melting magnesium scraps;     -   (b) forming a Ni—Al-misch metal three-phase alloy by adding Al,         misch metal, or Al and misch metal to the molten magnesium         scraps and stirring thereof;     -   (c) separating a precipitate and a floating matter of the         Ni—Al-misch metal three-phase alloy obtained in the step (b) by         stationing thereof for 10 min to 1 hour at 700° C. to 800° C.;         and     -   (d) casting a recycled magnesium alloy using the separated         floating matter.

In the method for preparing a recycled low-nickel magnesium alloy using magnesium scrap of the present invention, it is characterized that in the step (b), the Al is added in a ratio of 1 to 2 parts by weight, and the misch metal is added in a ratio of 1 to 2 parts by weight, based on 100 parts by weight of the magnesium scraps.

In the method for preparing a recycled low-nickel magnesium alloy using magnesium scrap of the present invention, it is characterized that when the magnesium scraps do not contain Al, the Al and the misch metal are added in a weight ratio of the Al and the misch metal (Al weight/misch metal weight) of 1 to 3 in the step (b).

In the method for preparing a recycled low-nickel magnesium alloy using magnesium scrap of the present invention, it is characterized that when the magnesium scraps contain Al, the misch metal is added in a weight ratio of the Al contained in the magnesium scraps and the misch metal (Al weight/misch metal weight) of 1 to 3 in the step (b).

In the method for preparing a recycled low-nickel magnesium alloy using magnesium scrap of the present invention, it is characterized that the misch metal is didymium misch metal, lanthanum-rich misch metal or Ce-rich misch metal.

In the method for preparing a recycled low-nickel magnesium alloy using magnesium scrap of the present invention, it is characterized that in the step (b), stirring is conducted one time, followed by stationing for 10 min to 30 min, and then conducted one more time.

In the method for preparing a recycled low-nickel magnesium alloy using magnesium scrap of the present invention, it is characterized that the Ni content of the recycled magnesium alloy in the step (d) is 0.6 weight % or less.

Advantageous Effects of the Invention

In the method for reducing nickel in the magnesium alloy of the present invention, the content of Ni, which works as impurities in a Mg—Ni alloy, can be reduced by adding Al and misch metal to a magnesium alloy, not by diluting Mg—Ni molten metal or by vacuum distillation method as a conventional method, thereby low-grade Mg scraps can be recycled.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of the invention taken in conjunction with the following accompanying drawings, which respectively show:

FIG. 1: pictures showing optical microscopic textures of the case that Al is added to the Mg—Ni alloy according to one embodiment of the present invention; and

FIG. 2: graphs of content analysis using XRF, of the case that misch metal or Al is added to the Mg—Ni alloy according to one embodiment of the present.

DETAILED DESCRIPTION OF THE INVENTION

The following Examples illustrate the invention and are not intended to limit the same.

Example

Because there is a big gap between the melting points of nickel and magnesium, first, a Mg-5 wt % Ni master alloy ingot was manufactured. After manufacturing a magnesium ingot of 5 wt %, Mg—Ni master alloy of about 2 kg was melted in a melting pot by using the ingot, and then zirconium (Zr), aluminum (Al) and misch metal (Misch metal, MN) were added thereto while changing the contents thereof as shown in the following Table 1, in order to reduce the nickel content.

In the process for manufacturing each sample, the elements of Table 1 were added, stirred about 1 min, held for 10 min, and then stirred again for 1 min. Then, for collecting samples, the resulting material was held at 720° C. for 30 min, the molten magnesium of 5 cc was collected from the upper part of the melting pot, and then the collected sample was poured into a mold and solidified, so as to manufacture a disk-type Mg—Ni specimen having average diameter of 29 mm and thickness of 7 to 10 mm.

TABLE 1 No. Misch Metal Al Example 1 1.00 0.50 Example 2 1.00 1.00 Example 3 1.00 2.00 Comparative Example 1 0.00 0.00 Comparative Example 2 0.50 0.00 Comparative Example 3 1.00 0.00

Test Example 1 Optical Microscope Observation

Each sample specimen manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, respectively, was observed by an optical microscope, and then the results are shown in FIG. 1.

In FIG. 1, (a) refers to the case of Comparative Example 1, in which misch metal of 0 wt % was added, (b) refers to the case of Comparative Example 2, in which misch metal of 0.5 wt % was added, (c) refers to the case of Comparative Example 3, in which misch metal of 1.0 wt % was added, and (d) refers to the case of Example 3, in which misch metal of 1.0 wt % and Al of 2.0 wt % were added.

In the sample of Example 3 containing misch metal of 1.0 wt % and Al of 2 wt % together, it can be observed that the second phase fraction of SDAS is significantly reduced.

Test Example 2 Ni Content Analysis Using XRF

The Ni contents in the samples manufactured in Examples and Comparative Examples were analyzed using XRF, and the results are shown in FIG. 2.

In FIG. 2, (a) refers to the change on the Ni content in the magnesium alloy depending on the amount of added misch metal, and (b) refers to the change on the Ni content in the magnesium alloy as the amount of added Al is increased, when misch metal of 1 wt % is added, and then the amount of Al added thereto is increased.

When only the misch metal was added in an amount of 0 to 1 wt %, there was a tendency that the Ni content is little increased instead, and then when aluminum was added in an amount of 1 to 2 wt % to 1 wt % misch metal, it can be confirmed that the Ni content is rapidly reduced.

When misch metal of 1 wt % and Al of 2 wt % are added, the Ni content was reduced to 0.521 wt %. Accordingly, the Ni content shows reduction rate of 48%, based on the initial Ni content.

INDUSTRIAL APPLICABILITY

In the method for reducing nickel in the magnesium alloy of the present invention, the content of Ni, which works as impurities in a Mg—Ni alloy, can be reduced by adding Al and misch metal to a magnesium alloy, not by diluting Mg—Ni molten metal or by vacuum distillation method as a conventional method, thereby low-grade Mg scraps can be recycled.

While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made and also fall within the scope of the invention as defined by the claims that follow. 

What is claimed is:
 1. A method for preparing a recycled low-nickel magnesium alloy using magnesium scraps, which comprises the steps of: (a) melting magnesium scraps; (b) forming a Ni—Al-misch metal three-phase alloy by adding Al, misch metal, or Al and misch metal at the same time to the molten magnesium scraps and stirring thereof; (c) separating a precipitate and a floating matter of the Ni—Al-misch metal three-phase alloy obtained in the step (b) by stationing thereof for 10 min to 1 hour at 700° C. to 800° C.; and (d) casting a recycled magnesium alloy using the separated floating matter.
 2. The method for preparing a recycled low-nickel magnesium alloy using magnesium scraps according to claim 1, wherein, in the step (b), the Al is added in a ratio of 1 to 2 parts by weight, and the misch metal is added in a ratio of 1 to 2 parts by weight, based on 100 parts by weight of the magnesium scraps.
 3. The method for preparing a recycled low-nickel magnesium alloy using magnesium scraps according to claim 2, wherein, when the magnesium scraps do not contain Al, the Al and the misch metal are added in a weight ratio of the Al and the misch metal (Al weight/misch metal weight) of 1 to 3 in the step (b).
 4. The method for preparing a recycled low-nickel magnesium alloy using magnesium scraps according to claim 1, wherein, when the magnesium scraps contain Al, the misch metal is added in a weight ratio of the Al contained in the magnesium scraps and the misch metal (Al weight/misch metal weight) of 1 to 3 in the step (b).
 5. The method for preparing a recycled low-nickel magnesium alloy using magnesium scraps according to claim 1, wherein the misch metal is didymium misch metal, lanthanum-rich misch metal or Ce-rich misch metal.
 6. The method for preparing a recycled low-nickel magnesium alloy using magnesium scraps according to claim 1, wherein, in the step (b), stirring is conducted one time, followed by stationing for 10 min to 30 min, and then conducted one more time.
 7. The method for preparing a recycled low-nickel magnesium alloy using magnesium scraps according to claim 1, wherein the Ni content of the recycled low-nickel magnesium alloy in the step (d) is 0.6 weight % or less. 